03 grand Marquis, 4.6
 

Good day folks. Have a drivability problem with this car. Idles smooth but under acceleration it lacks pickup and will backfire in the intake. If i let off the throttle slightly it will respond. Installed fuel gauge and it reads 32 psi at idle. On road test it will drop below 10 psi. Tested wiring to fuel pump module, all good. Checked fuel filter, good. Replaced fuel pump, same problem. Fuel pressure gauge does fluctuate quite a bit at idle. When i pinch the fuel hose adapter at the service valve the pressure will jump to 80 pls psi.. Coud it be the regulator which is part of the rail.? An.y advise would be appreciated

Fluctuating Fuel Pressure
 

Hello, and welcome to the Mercury Forums --
What you describe is a fluctuating fuel pressure -- and a failed Fuel Pressure Regulator.
The 95 MERC has a Mallory Adjustable Fuel Pressure Regulator (part # 4213), but the Mallory Adjustable Regulator WILL NOT FIT your 2003 model.
Fuel Pressure Regulators are now called "Fuel Pressure Dampers" -- which actually regulate the fuel pressure.
I think that you'll find the OEM Motorcraft regulator/damper to be plenty good for non-racing applications.

Motorcraft Part Available HERE :
Delphi (Identical) Part (but less expensive) is available HERE:

Sorry for the delay back. I replaced the fuel pressure regulator and the fuel damper. Still the same problem. It will still bog down under load. The fuel pressure gauge still drops down to almost zero under load. The fuel pressure now reads 26 psi at idle. If i pinch the service adapter on the rail side of the adapter the fuel pressure will climb up to 80 psi. When i disconnect the vacuum hose from the front right pressure regulator the vehicle performance is better but still bogs but if i slightly lift up the throttle it has power. Thanks again.

'03 Marquis Fuel Problem
 

This is getting freaky --
Your earlier post said you had 32 lbs. of Fuel Pressure.
Now it's down to 26 lbs.
Questions:
1. What do you mean when you say the Fuel Filter is "good" ?? If it's not a brand-new Motorcraft Fuel Filter, you can't assume that it's "good".
2. You replaced the Fuel Pressure "Regulator" AND the Fuel Pressure "Damper" -- with what ?? Gotta go with genuine Motorcraft fuel system parts, 'cause there's a LOT of junk parts on the market.
3. You replaced the Fuel Pump -- with a Motorcraft pump, or aftermarket ?? Once again, the Motorcraft part will be the best choice, with the Bosch #69128 as second choice, since the fuel system was a Bosch-Ford design.
I've used the Bosch fuel pump with great success, logging over 50,000 trouble-free miles.
Here's a link that MAY help you find the problem -- Good Luck !!
https://cimg6.ibsrv.net/gimg/www.mer...c09dc30ce5.jpg
Mallory Adjustable Fuel Pressure Regulator -- Set to 35 Lbs. @ 750 rpms., Hot Idle.

Thanks for the reply. The fuel damper was a ford oem part. The regulator was aftermarket and leaked. Cannot get a oem one anywhere here. Reinstalled the old one and plugged the vacuum hose for now. The fuel pump is a Bosch one. The fuel filter is oem also. The fuel pressure is now about 35psi and still drops to about 10psi under stiff acceleration. At least now it will take off with more power till i can find a oem regulator.

Fuel Pressure Woes
 

Your fuel system is not at all like The 95 MERC's , so I had to do some extra research in order to help diagnose your 2003's problems.
The 95 MERC has only a Fuel Pressure Regulator, and I've installed a Mallory Adjustable Regulator, which pretty much takes care of everything.
Your 2003 is another animal. It has a Fuel Pressure Regulator, a Fuel Pressure Damper, AND a Fuel Pressure SENSOR, which MAY be the source of your continuing problem.
Don't know why Motorcraft parts for the 2003 are so hard to find -- I found an installation video for the Sensor at CARID.com.
CARID offers a Standard Motor Products Sensor, part #FPS7. Standard is a reliable manufacturer of aftermarket products; comparable in quality to OEM.
https://cimg5.ibsrv.net/gimg/www.mer...502fd75fda.jpg
Bosch # 09725 Ignition Wires With Wire Separators Prevent Arcing and Misfires.

How and where can i list parts for sale? thanks